3. Calumnious, or reproachful; whatever has a tendency to injure the name, fame, or interest of another.

In short, it appears to mean any word or thing obscene, any thing that injures virtue, countenances vice, or scoffs at religion. In the parallel place, Colossians 4:6, the apostle exhorts that our speech may be seasoned with salt, to preserve it from putrefaction. See Kypke and Macknight.

But that which is good to the use of edifying - To be good for a thing is a Graecism, as well as an Anglicism, for, to be fit, proper, suitable, etc.; so Achilles Tatius, lib. iv. p. 231: Αγαθον εις φιλιαν οιδα σε· I know thee to be good (formed) for friendship. And Appian, de Bell. Hisp., p. 439, terms both the Scipios, Ανδρας ες παντα αγαθους γενομενους, men who were good (suitable) for all things. And also Lucian, in Toxari, p. 53: Ου μονον αρα τοξευειν αγαθοι ησαν Σκυθαι· The Scythians were not good (expert) in archery only. See Kypke, from whom Iquote.

That it may minister grace - Ἱνα δῳ χαριν. This may be understood thus:

1. Let your conversation be pure, wise, and holy, that it may he the means of conveying grace, or Divine influences, to them that hear.

2. Let it be such as to be grateful or acceptable to the hearers. This is the meaning of Ἱνα δῳ χαριν in some of the most correct Greek writers. Never wound modesty, truth, or religion with your discourse; endeavor to edify those with whom you converse; and if possible, speak so as to please them.

Barnes's Commentary
on Ephesians 4 :29

Let no corrupt communication proceed - see the notes on 1 Corinthians 15:33. The word rendered "corrupt" (σαπρὸς sapros) means bad, decayed, rotten, and is applied to putrid vegetable or animal substances. Then it is applied to a tree that is of a useless character, that produces no good fruit; Matthew 7:17. Then it is used in a moral sense, as our word "corrupt" is, to denote that which is depraved, evil. contaminating, and may denote here anything that is obscene, offensive, or that tends to corrupt others. The importance of this admonition will be appreciated when it is remembered:

(1) that such obscene and filthy conversation prevailed everywhere, and does still among the pagan. So general is this, that at almost every missionary station it has been found that the common conversation is so corrupt and defiling that missionaries have felt it necessary to send their children home to be educated, in order to secure them from the contaminating influence of those around them.

(2) those who have had the misfortune to be familiar with the common conversation of the lower classes in any community, and especially with the conversation of young men, will see the importance of this admonition. Scarcely anything can be conceived more corrupt or corrupting, than that which often prevails among young men - and even young men in the academies and colleges of this land,

(3) its importance will be seen from the "influence" of such corrupt communications. "The passage of an impure thought through the mind leaves pollution behind it;" the expression of such a thought deepens the pollution on the soul, and corrupts others. It is like retaining an offensive carcase above ground, to pollute the air, and to diffuse pestilence and death, which should at once be buried out of sight. A Christian should be pure in his conversation. His Master was pure. His God is pure. The heaven to which he goes is pure. The religion which he professes is pure. Never should he indulge himself in an obscene allusion: never should he retail anecdotes of an obscene character, or smile when they are retailed by others. Never should he indulge in a jest having a double meaning; never should be listen to a song of this character. If those with whom he associates have not sufficient respect for themselves and him to abstain from such corrupt and corrupting allusions, he should at once leave them.

But that which is good to the use of edifying - Margin, to edify profitably." Greek, "to useful edification:" that is, adapted to instruct, counsel, and comfort others; to promote their intelligence anti purity. Speech is an invaluable gift; a blessing of inestimable worth. We may so speak as "always" to do good to others. We may give them some information which they have not; impart some consolation which they need; elicit some truth by friendly discussion which we did not know before, or recall by friendly admonition those who are in danger of going astray. He who talks for the mere sake of talking will say many foolish things; he whose great aim in life is to benefit others, will not be likely to say that which he will have occasion to regret; compare Matthew 12:36; Ecclesiastes 5:2; Proverbs 10:19; James 1:19.

Wesley's Commentary
on Ephesians 4 :29

4:29 But that which is good - Profitable to the speaker and hearers. To the use of edifying - To forward them in repentance, faith, or holiness. That it may minister grace - Be a means of conveying more grace into their hearts. Hence we learn, what discourse is corrupt, as it were stinking in the nostrils of God; namely, all that is not profitable, not edifying, not apt to minister grace to the hearers.